1. The Field of the Invention
The present invention relates to forming multicomponent nanoparticles. In particular, the present invention relates to controlling the dispersion of two or more components to make nanoparticles where two or more different components are desirably distributed within the nanoparticles.
2. The Relevant Technology
Nanoparticles are becoming increasingly more important in many industrial processes and products. Nanoparticles find use in a variety of applications, including catalysis and nanomaterials. Catalytic applications include uses for both supported and unsupported nanoparticles of various components, including precious metals, base metals, and oxides. Nanomaterials applications include uses for light blocking, pigmentation, UV absorption, antimicrobial activity, chemical mechanical polishing, and others.
While useful nanoparticles may at times include only a single component (element or compound), it is often the case that advantageous properties can be achieved when the nanoparticles contain two or more distinct components to form a multicomponent particle. Combinations of two or more metals can have a variety of beneficial effects. In the case of catalysts, they can modify the catalytic activity to improve an important performance parameter such as activity or selectivity, or they may make the catalytic nanoparticle more resistant to some deleterious effect such as chemical poisoning or mechanical attrition. In the case of nanomaterials, the inclusion of two or more components can add additional functionality to the particles, such as combining light blocking function with UV absorption or anti-microbial activity. Alternatively, additional components may stabilize or strengthen the nanoparticles.
While there is a strong motivation for producing multicomponent nanoparticles, it is often difficult to create uniform compositions containing two or more unlike components. This problem is particularly true of nanoparticles. Recently, academia and industry have made significant advancements toward making very small particles. In some cases, the sizes of the particles are near or below 1 nanometer.
While nanometer sized particles are very advantageous for producing desired properties such as increased catalytic activity and unique material properties, small particle sizes can make it very difficult to create multicomponent nanoparticles. One reason for this difficulty is because similar or like elements or compounds have a greater affinity to combine and form particles with themselves, rather than mixing with other components. This leads to the tendency for multicomponent mixtures to result in the formation of two or more distinct particle compositions, some relatively rich in certain components, others relatively depleted or devoid of one or more components.
Particles are typically formed according to the thermodynamics between the two or more components. The chance of finding both components of a multicomponent particle in a single particle depends on the size of the particles. Where the particles are relatively large, the probability is higher that two dissimilar components can be compounded within a single particle and/or form an alloy. As the size of the particles decreases, however, the chance of finding both components within a single particle decreases dramatically. At the nanometer scale, it is virtually impossible to compound two or more dissimilar elements using known procedures. Particles tend to be all of one component or another.
Part of the problem with forming multicomponent nano-sized particles is that most methods used to form nano-sized particles are performed at relatively low temperatures since high temperatures causes nanoparticles to sinter or agglomerate to form larger particles. Unfortunately, at such low temperatures, the thermodynamics of nanoparticle formation favors formation of single-component particles as described above. Consequently, conventional particle formation methods are not able to form nano-sized particles containing two or more components that are uniformly distributed in each particle.
Another factor that significantly affects the uniformity of multicomponent particles is the dissimilarity of the components. For example, two noble metals such as palladium and platinum are typically more easily combined together within particles because their electronic and chemical properties are similar. In contrast, a noble metal such as platinum and a base metal such as iron have different electronic and chemical properties and are thus much more difficult to compound. In many cases, compounding dissimilar components does not produce a viable nanoparticle because of the lack of uniformity in the distribution of the components. This is particularly true for catalyst nanoparticles that require alloying to generate a desired catalytic performance.
Therefore, what are needed are multicomponent nanoparticles where different nanoparticle components are more evenly dispersed between the particles. Furthermore, what is needed is a process that can compound the different components together without destroying the nanometer size of the particles.